The present invention relates to an arrangement for controlling an automatic selector device of a change-speed gearbox of a motor vehicle, comprising two selecting elements, each comprising a selecting actuator operatable by pressure medium and usable for engagement and an associated frictional selecting connection (clutch or brake) disengageable again by spring force.
DE 41 17 736 C1 shows an arrangement in which the first multi-way valve arrangement, which is connected to the pressure system that can be put under system pressure and to the return line, can be switched into one of its end positions by a spring return and into its other position by the control pressure of an electromagnetic control valve that can be activated by the electronic control unit. This also applies to the second multi-way valve arrangement, which is connected to the selecting actuators and the two other pressure systems and has associated spring returns and a second electromagnetic control valve connected thereto. The two-times-two possible positions of these four valve arrangements define the four selector conditions, i.e two non-transient and two transient. These selector conditions can be selected in any desired sequence by the control unit using the two electromagnetic control valves.
DE 41 32 873 C2 describes an automatic selector device of a change-speed gearbox of the epicyclic type which operates with a frictional selector (i.e, clutch or brake) which can be engaged by a selecting actuator of the axial piston type and is located between two transmission elements which can rotate relative to one another. A selector valve which applies pressure to the selecting actuator and has an electromagnetic switch-over control valve, is controllable by an electronic control unit for switching over the selector valve. Both the selector valve and the switch-over control valve can each be switched between a rest position selectable by spring force and a working position. The selecting actuator is connected in the rest position of the selector valve to a pressure-relieved null connection whereas, in the working position, it is connected to a system-pressure line carrying a controlled system pressure. A selector-valve control connection used for the switch-over to the rest position is connected in the rest position of the switch-over control valve to a pressure-relieved null connection. In the working position, the switch-over control valve is connected to a control-pressure feed line carrying a control pressure.
In this latter known selector device, care is taken to ensure that the selecting actuator actuated at a particular time remains subjected to working pressure even if the electric power supply fails. When the engine is switched off, the selector device should assume a position such that, when the engine is restarted, the selecting actuators remain unpressurized. For this purpose, the arrangement in the known selector device is such that the selector valve can also be actuated into its rest position by the control pressure of the switch-over control valve and can be actuated into its working position by a control pressure dependent on the pressure of the selecting actuator and has control connections for this purpose. Moreover, the switch-over control valve is moved into its working position only in phases whereas, in the non-transient condition, i.e. in the completely engaged and in the completely disengaged condition, of the selector it is in its rest position.
In this known device, a control valve has a valve connection for a control pressure line leading to the control connection of the selector valve for the purpose of actuating it into its working position, a valve connection for a control pressure line leading to the control connection of the selector valve for the purpose of actuating it into the rest position, a valve connection for a control pressure line leading to the switch-over control valve and a valve connection for pressure relief. The control valve can be switched between a rest position, on one hand, in which the valve connection for the control pressure line for actuating the selector valve into its rest position is connected to the valve connection for pressure relief whereas the valve connection for the control pressure line for actuating the selector valve into its working position is connected to the valve connection for the control pressure line leading to the switch-over control valve, and a working position, on the other hand, in which the valve connection for the control pressure line for actuating the selector valve into the rest position is connected to the valve connection for the control pressure line leading to the switch-over control valve and the valve connection for the control pressure line for actuating the selector valve into its working position is connected to the valve connection for pressure relief. The control valve is switched over in such a way, as a function of the condition of the selector, that, in one non-transient condition of the selector, the valve connection of the control valve for the control pressure line leading to the switch-over control valve is in each case necessarily connected to the valve connection for the control pressure line for switching the selector valve into the position in which it moves the selector into the other non-transient condition.
In this known selector device, the switch-over control valve is always in its rest position in the non-transient condition of the selector apparatus. As a result, a failure of the electronics or of the power does not change anything as regards the selector condition. In the disengaged condition of the selector apparatus, the selector valve is held in its rest position by spring force and, in the engaged condition, is held in its working position by the self-retention effect of the relevant control pressure, which is dependent on the pressure of the selecting actuator. As a function of the respective instantaneous non-transient condition of the selector apparatus, the control valve is always moved in advance into that position in which, on excitation of the switch-over control valve, the selector valve will be switched into the position for the other selector condition, i.e. not the instantaneous non-transient selector condition. When the engine is switched off, the pressure supply is also switched off, and as a result the selector valve and the control valve are also actuated into the respective rest position by spring force. Accordingly, the selecting actuators remain unpressurized when the engine is restarted.
The gears of an automatic speed-change gearbox are selected by the selective activation of frictional selecting connections (e.g., clutches, brakes). A distinction can be drawn between two conditions: where the selecting connections are fully engaged or disengaged (non-transient phase; gear selected) or where they are engaged or disengaged in a defined manner for a gear change (selecting phase). In more recent automatic transmissions, the selection signals for activation are output by an electronic control unit. The hydraulic part of the control system is likewise assigned certain logical functions and furthermore serves to produce power for the selecting actuators for the engagement of the frictional selecting connections.
In an arrangement for controlling an automatic selector device of a change-speed gearbox, two frictional selecting connections can be engaged and disengaged in a controlled manner, in particular alternately, or their selecting actuators can be connected to the pressure system that can be put under system pressure or to the pressure-relieved return line or directly to a pressure-medium collecting tank. Here, the selecting actuator of the selecting connection to be engaged can be subjected to a controlled working pressure and the selecting actuator of the selecting connection to be disengaged can be subjected to a controlled outlet pressure. To construct a control system for the automatic selector device of a complete multi-speed change-speed gearbox, a correspondingly large number of arrangements, each with two alternately operating selecting connections, are thus required.
An object of the present invention is to provide a control system for the automatic selector device of a multi-speed change-speed gearbox which is distinguished by a small constructional outlay for a given number of forward gears.
The foregoing object has been achieved according to the present invention in an arrangement for controlling an automatic selector device by providing that the control pressure for the first multi-way valve arrangement, which is operatively associated with the pressure system subjectable to system pressure and to the return line, is one of equal to and proportional to a difference between pressures in the selecting elements. In the second and fourth transient selector conditions, the working pressure is controllable with a rising characteristic from a low initial value and the outlet pressure is controllable with a falling characteristic from a high initial value. The working pressures intersect with variations thereof with respect to time. The first multi-way valve arrangement is subjected to control pressure in a direction of the pressure difference so that, at the end of the transient selector condition, the first multi-way valve arrangement is in a position in which the selecting element connected to the pressure system for the working pressure during the transient selector condition is connected in a subsequent non-transient selector condition to the pressure system subjectable to system pressure. In a deenergized and unpressurized condition, the multi-way valve arrangements are held continually by respective spring returns in that position in which one and the same predetermined selecting element is connected to the pressure system subjectable to system pressure, and the second multi-way valve arrangement which is associated with the selecting elements is actuatable by the control pressure of the connected electromagnetic control valve into position thereof corresponding to the second transient selector condition and, by the spring returns into a position thereof corresponding to the third non-transient selector condition.
In the arrangement according to the invention, only a single electromagnetic control valve controllable by the electronic control unit is required to control the two non-transient selector conditions and the two transient selector conditions--that is, in total, to control four selector conditions when changing the two selecting elements. As a result, the constructional outlay for a control system with a required number of n arrangements in accordance with the present invention is considerably reduced, namely by n electromagnetic control valves.
The present invention provides an interrelationship between two multi-way valve arrangements as regards their respective starting positions in the deenergized and unpressurized condition and the automatic switching over of the first multi-way valve arrangement, which is connected to the pressure system that can be put under system pressure and to the return line, as a function of the difference between the pressures in the two selecting actuators. This ensures that the four selector conditions always occur in the same sequence and can be controlled simply by the change in level and duration of a single binary control signal used to switch over the second multi-way valve arrangement which is connected to the selecting actuators.
The electromagnetic control valve influenced by the electronic control unit is, in its deenergized initial position, in both non-transient selector conditions. Consequently, if the electronic control unit fails during the journey, the instantaneous non-transient condition is maintained, i.e. the respectively selected gear is retained. Thus, the triggering of any critical driving conditions in the event of this malfunction is prevented.
The second multi-way valve arrangement, the multi-way valve arrangement connected to the selecting actuators and in the form of an individual multi-way valve, has a separately assigned position for each of the two transient selector conditions. The valve can be switched into this position by the electromagnetic control valve in dependence on two position control valves. One position control valve is connected to the electromagnetic control valve and operates as a function of the position of the first multi-way valve arrangement, the multi-way valve arrangement connected to the pressure system that can be put under system pressure and to the return line. The other position control valve operates in dependence on a selector valve which is connected, inter alia, to the selecting elements.
The position control valve connected to the electromagnetic control valve and the first multi-way valve arrangement can further be combined to give a single multi-way valve.
It is furthermore within the scope of the present invention for the selector valve connected to the selecting elements and the dependent position control valve to be combined structurally in a way which provides a single multi-way valve. Therefore, a total of only two multi-way valves is needed for the first and the second multi-way valve arrangement, resulting in substantial structural simplification.
In another embodiment of the arrangement for controlling an automatic selector device according to the present invention, a two-position multi-way selector valve connected to the selecting actuators and a two-position multi-way control valve connected to the pressure systems for the working pressure and the outlet pressure are used for the second multi-way valve arrangement.
This other embodiment is therefore distinguished by shorter directional control valves of the axial-piston type which can often be accommodated in a more favorable manner in a compact control casing and guided with greater precision in axially displaceable fashion.
In order to ensure in this second embodiment that the control valve connected to the pressure systems for the working pressure and the outlet pressure is not switched over before the completion of the transient selector condition in which the selecting actuator connected to the return line in the first selector condition is subjected to the outlet pressure, a self-retention function is provided. The control valve connected to the pressure systems for the working pressure and for the outlet pressure and the dependent position control valve for the retention pressure can, in a structurally simplified way, be combined into a single multi-way valve. Likewise, the selector valve connected to the selecting actuators and the dependent position control valve for the retention pressure can, also in a structurally simplified way, be combined to give a single multi-way valve.